A membrane may be defined as a separation or transfer of a certain material from the others, of which the properties are different from that of the above material, by using its semi-permeable property. In addition, its separation efficiency can be improved by using a property, such as charge repulsion, solubility, diffusion rate, etc., in addition to a separation or transfer of at least any size, simply.
A study on the membrane has been done by using a material, such as a polymer, a ceramic, a metal, etc., and a study on the development of the membrane has supported the activation of membrane industry, and also has been instrumental in developing relevant industries.
The polymer membrane has been generally used to separate a mixture gas, such as O2/N2, CO2/CH4, CO2/N2, olefin/paraffin, etc. Especially, the polymer membrane has advantages that it can improve the degree of separation because of its hydrophilicity or hydrophobicity and is of great advantage to separate a specific material, but also has disadvantages that it has poor durability, and is also vulnerable to a solvent, hydration, UV, etc.
In addition, an inorganic membrane, such as a ceramic, a metal, etc., increases the resistances to high pressure, poor chemicals, etc., but it remains too expensive and has a relatively small void ratio and filtration rate. Accordingly, there are various limits on using it.
Above this, a study using an ionic liquid is proceeding and technological trends in the ionic liquid are as follows.
Covalent Associates Incorporated asserts their right to properties and explanations of cation and anion of an ionic liquid by suggesting the ionic liquid including various cations and anions with improved properties for using in non-aqueous battery, electrochemical capacity, electrodeposition, catalysis, and chemical separation, as disclosed in ‘Hydrophobic Ionic Liquid’ of US Patent No. U.S. Pat. No. 5,827,602 (Oct. 27, 1998).
University of Notre Dame du Lac discloses a method of separating gas from a mixture gas, including contacting the mixture gas with a liquid ionic compound including nitrogen-containing heterocyclic cation, as disclosed in US Patent No. U.S. Pat. No. 6,579,343 (filed on Apr. 1, 2002).
RIKEN KEIKI discloses a use of an ionic liquid as electrolyte by suggesting a use of the ionic liquid as electrolyte for an electrochemical gas sensor of continuity, in which a plurality of electrode use mutually electrolyte, as disclosed in Japanese Publication No. JP2004333163 (filed on Apr. 30, 2003).
CHEVRON USA discloses a method of removing CO2 by separating CO2 using an ionic liquid as an absorbent in the process of removing CO2, as disclosed in U.S. Publication No. US20050129598 (filed on Dec. 16, 2003).
THE BOC GROUP discloses a method of removing an acidic gas included in a supply gas stream as a monolithic substrate coated with an ionic liquid or an ionic liquid mixture, and also imidazolium, pyridium, pyrrolidium, ammonium, phosphonium, sulfonium, or guanidium as an example of the ionic liquid, as disclosed in International Patent Publication No. WO07101397 (filed on Mar. 5, 2007).
Korea Advanced Institute of Science and Technology discloses a facilitated transport membrane for a separation of alkane-based hydrocarbon consisting of a porous support membrane and a solid polymer electrolyte layer consisting of transition metal salts, a polymer, and an ionic liquid, as disclosed in U.S. Publication No. 20050150383 (filed on Dec. 13, 2004).
As mentioned above, a study on applying an ionic liquid to a membrane is proceeding and also a study on a separation of CO2/N2 through a supported ionic liquid membrane (SILM) using high CO2 solubility of the ionic liquid has been conducted. However, the ionic liquid membrane has a disadvantage that it is impossible to be used in an actual gas separation process due to a problem of safety that filters the ionic liquid through the membrane at a pressure of at least 0.2 atm.
Accordingly, it is needed to develop a membrane that has durability even at more than normal pressure, and also allows its selectivity and permeability to be improved.